Insulating glass units for use in windows or doors or the like commonly comprise two or more parallel glass panes that are separated from one another by spacers along their edges. Various multiple-pane configurations are known to the art, and such configurations may include two, three or more panes. Certain of these configurations have employed sheets of plastic in parallel, spaced relation to the glass panes. If a multiple pane glass unit is to be assembled with a plastic sheet held in spaced relationship between two glass panes, the unit may be manufactured by applying a marginal spacer along the edges of one glass pane, the spacer extending away from the plane of the pane, adherring a heat-shrinkable film to the spacer, and then heat-shrinking the film to draw the film taut and flat. The second pane, also provided with a marginal spacer, is then attached, the film becoming sandwiched between the opposed marginal spacers of the two panes. In another embodiment, the film may be grasped by small springs that are held by or form a part of spacers separating the two glass panes from one another. Generally unbreakable mirrors may be formed by adherring a marginal spacer about the periphery of a sheet of plywood or the like, then adherring a heat-shrinkable, silvered plastic film to the spacers, and then heat-shrinking the film so that it becomes taut and flat to provide a mirrored surface.
In each of the described embodiments employing heat-shrinkable plastic film, the film is stretched over spacers held at the edge of a stiff pane or board or the like, and the plastic film is then heated directly, typically by hot air. For multiple-pane glass units in which the plastic film is to be employed as an internal sheet between but spaced from parallel glass panes, the manufacturing methods cited above have been found difficult and time consuming, and require piece-meal construction methods.